The invention relates generally to the art of graphic generators, and more particularly concerns an improvement in three dimension graphic generators.
In general, the basic concept of a three dimension graphic generator is known. In such graphic generators, as with two dimension graphic generators, information from a sensor, such as a camera, is typically displayed in the form of a raster comprising a vertical succession of horizontal lines. One dimension, or image variable, of the display is along the horizontal axis and referred to as image width, produced by the horizontal length of the raster lines, while a second dimension, or image variable, is along the vertical axis and referred to as image height, produced by the vertical succession of raster lines. A third dimension, or image variable, referred to as the image depth, is the intensity information of the display, which, instead of being a variable in each line of the display, as is the case with a television display for instance, is used as a deflection signal, superimposed on the vertical axis. The intensity of each line in the display thus does not change, although it appears to the viewer to change because of the variation in the deflection of each line in accordance with the intensity information.
FIG. 1a is a diagram which shows several lines 10a-10d of a very simplified raster. Each raster line has the same intensity over its entire length, but varies in vertical position or deflection in accordance with the intensity information of the input data for that line. An intensity variation is shown in each line as portions 10a'-10d'.
The three dimension feature of such generators is obtained by rotating the raster lines through a selected angle while maintaining the orientation of the intensity information which has been superimposed on the vertical axis undisturbed. The intensity information thus becomes a reference point around which the raster lines are rotated.
The viewpoint of the particular scene being displayed thus appears to change, i.e. the scene appears now to be viewed from a different angle, without a change in the sensor viewpoint or the input data. Such a graphic generator operates in three dimensions, because the display can be manipulated electronically so that the scene appears to be viewed at different angles, without changing the viewpoint of the sensor.
With such an apparatus, the raster lines of FIG. 1a, when rotated through an angle a, appear as shown in FIG. 1b, in which the lines 10a-10d are rotated, except for the intensity information portions 10a'-10d', which maintain their original orientation. It can be seen from an inspection of FIG. 1b that rotation of the raster lines about the intensity information will change the apparent view of the display without changing the viewpoint of the sensor. Hence, the data from the sensor appears to be three-dimensional, as the image appears to have true depth. Such generators are in general known in the art. One such generator is available from International Imaging Systems/I.sup.2 S of Mountain View, Calif. 94023.
However, existing three dimension graphic generators have two very significant disadvantages where heretofore have limited their usage. First, an 11 bit word has been heretofore used to describe each resolution element or point on the display, which requires a very large amount of memory space. A typical raster that displays a million resolution elements will thus require a memory capacity of eleven million bits. This is accomplished presently by converting the data to analog form, recording it on a drum memory and then utilizing it as a vertical dimension summation on the synchronized raster.
The second disadvantage concerns the so-called hidden line problem inherent in the generation of the image. The hidden line problem concerns those portions of individual raster lines which should not be present in a given image because they are in reality hidden by another part of the image. Hidden lines obscure the true data of the real image and hence, are undesirable. The large amounts of data required to form the three dimension image, as noted above, however, make it impractical to correct the hidden lines in current generators.
In view of the above, it is an object of the present invention to provide a graphic generator which solves one or more of the problems of the prior art discussed above.
It is another object of the present invention to provide such a graphic generator which reduces the size of the memory necessary to generate a three dimension image.
It is a further object of the present invention to provide such a graphic generator which presents a truer image by solving the hidden line problem.
It is an additional object of the present invention to provide such a graphic generator which produces such a truer image in a relatively short period of time.